You might be able to do this through the options.
Select a directory that has the songs you wish to share with the outside world.
When you have decided what you want to share select that directory in LimeWire.
The rest of your mp3's can be anywhere (in a directory called C:\Music) that's where I have my files that I don't wish to share at this time. But you can select any directory as the shared directory including that one if you wish. The only thing that's a bit different is where Limewire keeps it's downloaded songs. What they call your Library is the directory that you have chosen to share with other users. (mine is called Music Shared) I have about 300 songs in this directory but the other 2000 are in a separate directory just called "Music". The reason I have separate directories is because if you have all your files shared your system can some times become bogged down with people wanting to get at the multitude of songs you may have collected over a period of years.
I find it better to keep my songs that I've just downloaded in a separate folder called: Downloaded Music. but I have selected a different folder to be the one I share with other people. This is all setup through the options of LimeWire and I've had no problems having separate folders for the 3 different functions.

I have itunes & use limewire for music but i am having trouble getting my limewire libary to import to my itunes libary